1. Field of the Invention
The present invention relates to an image combining apparatus for combining a plurality of photographed images by adjusting positions thereof.
2. Description of the Related Art
In recent years, in the case of combining a plurality of photographed images, as a method of detecting a motion vector of the image for a correction of image blurring or the like, a block matching method or a correlation method based on a correlation operation has been known. According to the block matching method, an image signal which is input is divided into a plurality of blocks each having a proper size (for example, 8 pixels×8 lines) and a difference of a pixel value between a current field (or frame) and a previous field is calculated on this block basis. A block of the previous field having a higher correlation to a block of the current field is searched for on the basis of the difference, and a motion vector of the block is obtained as a relative positional difference between images.
For example, each of the Official Gazettes of Japanese Patent Application Laid-Open Nos. H08-251474 and 2009-188837 discloses a selecting method of a motion vector and a weighting method. The Official Gazette of Japanese Patent Application Laid-Open No. H08-251474 discloses a selecting method of a representative motion vector (motion vector of the whole image) based on an index such as a size of an image area or vector stability. The Official Gazette of Japanese Patent Application Laid-Open No. 2009-188837 discloses a method of detecting an object area and calculating such a motion vector (correction vector) as to reduce a blurring of a main object (object to be photographed) in consideration of importance of the main object.
In the related art, in the case of combining a plurality of photographed images, first, a motion vector is detected in a predetermined area of an image in order to make a correction of the image blurring or the like, the detected motion vector is weighted, and a vector for position adjustment is generated by combining the weighted motion vectors. As a weighting in this case, a weighting corresponding to features of an image area or to an object area in which the object is detected is used.
Upon photographing, a detection of the object, focus control, proper exposure control, and the like are performed in accordance with the operation (for example, half-depression) of a first shutter switch which is executed by the operator, and the main photographing is performed in accordance with the operation (for example, full-depression) of a second shutter switch. In this case, generally, information such as object position of the photographed image, features of the object, and the like is obtained when the operator operates the first shutter switch to lock the object.
FIGS. 1 and 2 are diagrams for explaining a relation between a generation of weightings of a motion vector by the method of the related art and the operations of the first and second shutter switches.
When the operator operates the first shutter switch, AF control and AE control (101, 201) are performed and an object lock (102, 202) (AF, AE lock state) is obtained. Subsequently, when the operator operates the second shutter switch, a still image photographing (103, 203) is performed. At this time, an elapsed time from the operation of the first shutter switch is denoted with the numerals 111 and 211. A photographing angle of view at a point of time of the operation of the first shutter switch is denoted with the numerals 104 and 204. An object (109, 209) and a detected object area (107, 207) are shown. The detected object area (107, 207) is, for example, a main object area detected at the time of the AF control or AE control. A photographing angle of view at a point of time of the operation of the second shutter switch and the object lock (102, 202) is denoted with the numerals 105 and 205. An actual object at this time is denoted with the numerals 110 and 210 and a detected object area is denoted with the numerals 108 and 208. A weighting table of the motion vector for position adjustment at the time of combination is denoted with the numerals 106 and 206. In the table, the larger a numeral is, the larger a weighting of the motion vector in this area is. The smaller a numeral is, the smaller a weighting becomes. The weighting table (106, 206) is generated on the basis of object information (position, size, features, and the like) at the point of time of the object lock (102, 202) and the larger weighting is applied to the object area.
When the elapsed time (lock state) from the operation of the first shutter switch to the operation of the second shutter switch is short as shown in the time 111, it is considered that the object 109 exists at almost the same position as that of the actual object 110 and is not so moved even after the elapse of time 111. Therefore, the weighting table 206 which is generated properly corresponds to the position of the actual object 110. However, when the elapsed time (lock state) from the operation of the first shutter switch to the operation of the second shutter switch is long as shown in the time 211, there is such a case where the object 209 is moved to the position of the actual object 210 after the elapse of time 211. In such a case, there is such a problem that the generated weighting table 206 of the motion vector which is generated does not properly correspond to the position of the actual object 210.